The present invention relates to a heat treatment apparatus such as a baking apparatus and a prebaking apparatus to be incorporated into a semiconductor manufacturing system for manufacturing a semiconductor device.
In a photolithography process for manufacturing a semiconductor device and an LCD, resist is coated on a substrate, and the resultant resist coating film is exposed to light and developed. Such a series of processing is carried out in a coating/developing system. The coating/developing system has heating sections such as a prebaking unit and a postbaking unit. Each of these heating sections has a hot plate with a built-in heater of a resistance heating type.
Recently, semiconductor device circuits have been miniaturized more and more. Their pattern wiring is formed in a width of the sub micron order. Under the circumstances, it has been strongly desired to control the heat treatment temperature of the photoresist film more accurately. The wafers W (objects to be treated) are usually treated in units (lots) each consisting of, e.g., 25 wafers. Each lot is processed under the same recipe (individual treatment program). Prebaking and postbaking are performed under heat treatment conditions according to individual recipes. The wafers belonging in the same lot are heated under the same conditions.
According to each of the recipes, the heat treatment temperature may be varied within such an acceptable range that the temperature will have no effect on a final semiconductor device. In other words, a desired temperature may differ from a heat treatment temperature in practice. When the wafer is treated with heat beyond the acceptable temperature range, a desired photoresist film cannot be obtained. Then, to obtain the desired photoresist film, a thermocouple is used for detecting the temperature of the hot plate. On the basis of the detected temperature, the power supply to the heater can be controlled in a feed-back manner. To describe more strictly, since the temperature of the entire hot plate is not uniform and varies with the passage of time, it is difficult to determine the temperature of the hot plate by a single thermocouple momentarily.